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  • 101.
    Booker, Ian Don
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stenberg, Pontus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sveinbjörnsson, Einar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Science Institute, University of Iceland, Reykjavik, Iceland.
    Donor and double donor transitions of the carbon vacancy related EH6/7 deep level in 4H-SiC2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 23, article id 235703Article in journal (Refereed)
    Abstract [en]

    Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6∕7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp 0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σn 2+(T) ≈ 1 × 10−14 cm2, σn +(T) ≈ 1 × 10−14 cm2, and σp 0(T) ≈ 9 × 10−18 cm2 for EH6 and σn 2+(T) ≈ 2 × 10−14 cm2, σn +(T) ≈ 2 × 10−14 cm2, σp 0(T) ≈ 1 × 10−20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6∕7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.

  • 102. Boström, Anders
    et al.
    Olsson, Peter
    Transmission and reflection of electromagnetic waves by an obstacle inside a waveguide1981In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 52, no 3, p. 1187-1196Article in journal (Refereed)
  • 103.
    Bottger, P. H. M.
    et al.
    Laboratory of Nanoscale Materials Science, EMPA, Dübendorf, Switzerland .
    Braginsky, L.
    Laboratory of Crystallography, ETH Zürich, Zürich, Switzerland.
    Shklover, V.
    Laboratory of Crystallography, ETH Zürich, Zürich, Switzerland.
    Lewin, Erik
    Laboratory of Nanoscale Materials Science, EMPA, Dübendorf, Switzerland .
    Patscheider, J.
    Laboratory of Nanoscale Materials Science, EMPA, Dübendorf, Switzerland .
    Cahill, D. G.
    Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois, USA .
    Sobiech, M.
    Oerlikon Balzers Coating AG, Balzers, Principality of Liechtenstein .
    Hard wear-resistant coatings with anisotropic thermal conductivity for high thermal load applications2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 1, p. 013507-Article in journal (Refereed)
    Abstract [en]

    High thermal load applications such as high speed dry cutting lead to high temperatures in the coated tool substrate that can soften the tool and high temperature gradients that can put stress on the coating/tool interface. In this work, theoretical considerations are presented for multilayer and graded protective coatings that can induce a significant anisotropy in their thermal conductivity. Solution of the heat equation shows that anisotropy of thermal conductivity has the potential to reduce temperatures and temperature gradients arising due to brief, localized heat at the coating surface ("hot-spots"). Experimental realization of high anisotropy is demonstrated in TiN/AlCrN multilayer coatings with variable layer thickness. In the coating with 50 nm bilayer periodicity, the highest anisotropy was obtained with a value of kappa(parallel to)/kappa(perpendicular to) = 3.0 +/- 0.9. Time-domain thermoreflectance is used to measure in-plane and cross-plane thermal conductivity of fabricated coatings. The observed high values of anisotropy of thermal conductivity are compared with theoretical predictions and its realisation is discussed with regard to the coating microstructure.

  • 104.
    Bouhafs, Chamseddine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Persson, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Tiberj, A.
    University of Montpellier 2, France.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Paillet, M.
    University of Montpellier 2, France.
    Zahab, A. -A.
    University of Montpellier 2, France.
    Landois, P.
    University of Montpellier 2, France.
    Juillaguet, S.
    University of Montpellier 2, France.
    Schoeche, S.
    University of Nebraska, NE 68588 USA; University of Nebraska, NE 68588 USA.
    Schubert, M.
    University of Nebraska, NE 68588 USA; University of Nebraska, NE 68588 USA.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 8, p. 085701-Article in journal (Refereed)
    Abstract [en]

    Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn. (C) 2015 AIP Publishing LLC.

  • 105. Bouhrara, M.
    et al.
    Saih, Y.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Goze-Bac, C.
    Abou-Hamad, E.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-resolution (13)C nuclear magnetic resonance evidence of phase transition of Rb,Cs-intercalated single-walled nanotubes2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 5, p. 054306-Article in journal (Refereed)
    Abstract [en]

    We present 13 C high-resolution magic-angle-turning (MAT) and magic angle spinning nuclear magnetic resonance data of Cs and Rb intercalated single walled carbon nanotubes. We find two distinct phases at different intercalation levels. A simple charge transfer is applicable at low intercalation level. The new phase at high intercalation level is accompanied by a hybridization of alkali (s) orbitals with the carbon (sp2) orbitals of the single walled nanotubes, which indicate bundle surface sites is the most probable alkali site.

  • 106.
    Brena, Barbara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Influence of ligands on the electronic and magnetic properties of Fe porphyrin in gas phase and on Cu(001)2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 17, article id 17B318Article in journal (Refereed)
    Abstract [en]

    A study of the adsorption of different axial ligands on Fe porphyrin (FeP), both isolated and adsorbed on Cu(001), was performed by means of Density Functional Theory. The electronic and magnetic properties of the adsorbed FeP resulted to be strongly influenced by the axial ligands considered, Cl and O. Cl induces an enhancement of the overall molecular magnetic moment of 3.0 mu(B) while O or O-2 leave the spin state of the molecule unchanged. The influence of the Cl in the electronic states was moreover studied by means of theoretical NEXAFS N K-edge, where the spectra of isolated FeP and FeP with Cl ligand were calculated. The adsorption of the FeP molecules on Cu(001) leads in case of Cl to a further increase of the magnetic moment due to strong deformation of the Fe-N bond.

  • 107.
    Brill, J. W.
    et al.
    University of Kentucky, KY 40506 USA.
    Shahi, Maryam
    University of Kentucky, KY 40506 USA.
    Payne, Marcia M.
    University of Kentucky, KY 40506 USA.
    Edberg, Jesper
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Yao, Y.
    University of Kentucky, KY 40506 USA.
    Crispin, Xavier
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Anthony, J. E.
    University of Kentucky, KY 40506 USA.
    Frequency-dependent photothermal measurement of transverse thermal diffusivity of organic semiconductors2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 23, p. 235501-Article in journal (Refereed)
    Abstract [en]

    We have used a photothermal technique, in which chopped light heats the front surface of a small (similar to 1 mm(2)) sample and the chopping frequency dependence of thermal radiation from the back surface is measured with a liquid-nitrogen-cooled infrared detector. In our system, the sample is placed directly in front of the detector within its dewar. Because the detector is also sensitive to some of the incident light, which leaks around or through the sample, measurements are made for the detector signal that is in quadrature with the chopped light. Results are presented for layered crystals of semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pn) and for papers of cellulose nanofibrils coated with semiconducting poly(3,4-ethylene-dioxythiophene): poly (styrene-sulfonate) (NFC-PEDOT). For NFC-PEDOT, we have found that the transverse diffusivity, smaller than the in-plane value, varies inversely with thickness, suggesting that texturing of the papers varies with thickness. For TIPS-pn, we have found that the interlayer diffusivity is an order of magnitude larger than the in-plane value, consistent with previous estimates, suggesting that low-frequency optical phonons, presumably associated with librations in the TIPS side groups, carry most of the heat. (C) 2015 AIP Publishing LLC.

  • 108.
    Broddefalk, A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Granberg, P
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Liu, HP
    Andersson, Y
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Magnetocrystalline anisotropy of (Fe1-xCox)(3)P1998In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 83, no 11, p. 6980-6982Article in journal (Other academic)
    Abstract [en]

    The magnetocrystalline anisotropy energy (MAE) of (Fe1-xCox)(3)P (x = 0, 0.1, 0.2, 0.33) has been studied in the temperature range 5 K-300 K. The compound crystallizes in a tetragonal structure with three non-equivalent metal sites and shows an easy plan

  • 109. Broitman, E.
    et al.
    Hellgren, N.
    Järrendahl, Kenneth
    Linköping University, The Institute of Technology.
    Johansson, M.P.
    Olafsson, S.
    Radnoczi, G.
    Radnóczi, G., Res. Inst. Tech. Phys. and Mat. Sci., P.O. Box 49, H-1525 Budapest, Hungary.
    Sundgren, J.-E.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Electrical and optical properties of CNx(0=x=0.25) films deposited by reactive magnetron sputtering2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 89, no 2, p. 1184-1190Article in journal (Refereed)
    Abstract [en]

    The electrical and optical properties of carbon-nitride CNx films (O=x=0.25) deposited by unbalanced reactive magnetron sputtering from a graphite target in mixed Ar/N2 discharges at a substrate temperature of 350°C have been investigated. Pure C films exhibit a dark conductivity at room temperature of 250 O-1 cm-1, which grows up to 250 O-1 cm-1 for CNx films with N content of 20%. For CNx films, temperature-dependent conductivity measurements suggest that two electron conduction processes exist in the investigated temperature range 130

  • 110.
    Bručas, Rimantas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Chalmers tekniska högskola.
    Hanson, M.
    Chalmers tekniska högskola.
    Gunnarsson, R.
    Chalmers tekniska högskola.
    Wahlström, E.
    van Kampen, Maarten
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Lidbaum, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Magnetic and transport properties of Ni81Fe19/Al2O3 granular multilayers approaching the superparamagnetic limit2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 7, p. 073907-Article in journal (Refereed)
    Abstract [en]

    The magnetic and transport properties of Ni81Fe 19/Al2O3 granular multilayer films were studied in relation to their structural properties as the nominal thickness t of the permalloy (Ni81Fe19) layer was varied near the percolation limit: in the range of 8≤t≤ 16 Å while keeping the nominal thickness of the Al2O3 layers constant at 16 Å. A good structural quality of the multilayers was demonstrated by low angle x-ray reflectivity measurements, and transmission electron microscopy showed the transition from continuous permalloy layers separated by aluminium oxide layers for t= 16 Å to metal grains dispersed in the insulator at t=8 Å. Magnetization measurements showed the gradual transition from ferromagnetic layers to superparamagnetic clusters and grains that successively become blocked as the temperature decreases. A strong correlation between transport and structural properties was observed in the temperature (T) dependence of the electrical resistance measured with the current in the plane in the range of 2 ≤T≤300 K: a gradual change of behavior from continuous permalloy layers with conducting interlayer connections for t=16 Å. to isolated permalloy grains in a dielectric for the film with t= 10 Å. The percolation occurs between 12 and 10 Å, as deduced both from the magnetic and resistive properties. The discontinuous metal films were analyzed within models for thermally assisted tunneling, yielding estimates of the tunneling barrier for intralayer conduction of about 20 meV for t= 10 Å. A significant magnetic field dependence of the resistance increasing with decreasing temperature was observed in all samples.

  • 111. Buixaderas, E.
    et al.
    Bovtun, V.
    Kempa, M.
    Savinov, M.
    Nuzhnyy, D.
    Kadlec, F.
    Vanek, P.
    Petzelt, J.
    Eriksson, M.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Broadband dielectric response and grain-size effect in K0.5Na0.5NbO3 ceramics2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, no 1, p. 14111-Article in journal (Refereed)
    Abstract [en]

    Dielectric spectra of two K0.5Na0.5NbO3 ceramics with different grain sizes (10 and 0.5 mu m) were measured from 10(2) to 10(14) Hz in a broad temperature range. The sequence of first-order phase transitions (cubic-tetragonal-orthorhombic-rhombohedral) was detected by differential scanning calorimetry, dielectric spectroscopy, and time-domain terahertz spectroscopy. The grain size affects all the phase transitions, which are more smeared in the small-grain sample. In the large-grain ceramics, two well-separated near-Debye relaxations are seen in the tetragonal phase, which suddenly merge on cooling across the tetragonal-orthorhombic transition, and on further cooling the lower-frequency relaxation strongly broadens. On reducing the grain size, the higher-frequency relaxation shifts from similar to 1 to similar to 20 GHz and the lower-frequency one strongly broadens. Without quantitative understanding, these effects could be assigned to domain-wall dynamics and its temperature and grain-size dependences. Similar to pure KNbO3, an overlapped central-mode-soft-mode type excitation was detected in the terahertz range related to the effective hopping and oscillations of the off-centered Nb ions in a multiwell potential.

  • 112.
    Burnett, Tim L
    et al.
    National Phys Lab, England .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kazakova, Olga
    National Phys Lab, England .
    Identification of epitaxial graphene domains and adsorbed species in ambient conditions using quantified topography measurements2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 5, p. 054308-Article in journal (Refereed)
    Abstract [en]

    We discuss general limitations of topographical studies of epitaxial graphene in ambient conditions, in particular, when an accurate determination of the layers thickness is required. We demonstrate that the histogram method is the most accurate for measurements of small vertical distances (andlt;0.5 nm) and generally should be applied to epitaxial graphene and similar types of samples in order to get the correct and reproducible values. Experimental determination of the step height between different domains of epitaxial graphene shows excellent agreement with the predicted values once the adsorption of a 2D monolayer is taken into account on top of the one layer graphene. In contrast to general limitations of AFM topography, electrostatic force microscopy imaging allows a straightforward identification of domains of epitaxial graphene of different thickness.

  • 113.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Rudko, G. Yu.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Toropov, A. A.
    Sorokin, S. V.
    Ivanov, S. V.
    Kopev, P. S.
    Resonant suppression of exciton spin relaxation in Zn0.96Mn0.04Se/CdSe superlattices2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 10, p. 7352-Article in journal (Refereed)
    Abstract [en]

     Spin relaxation processes in strained Zn0.96Mn0.04Se/CdSe superlattices are studied in detail by using hot photoluminescence combined with tunable excitation spectroscopy. A drastic enhancement in occupation of the upper-lying |+1/2,-3/2> state of the heavy-hole excitons is observed when excitation photon energy is resonantly tuned near an integer number of the LO phonon energy above the |+1/2,-3/2> state. Assuming the Boltzmann distribution between the excitonic states, the spin temperature of the excitons is deduced to be as high as 85 K, well above the lattice temperature of 2 K. The observed behavior provides experimental evidence for a surprisingly strong suppression of spin relaxation from the upper spin-split excitonic branch for small values of wave vector.

  • 114.
    Calamba, Katherine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Univ Lorraine, France.
    Pierson, J. F.
    Univ Lorraine, France.
    Bruyere, S.
    Univ Lorraine, France.
    Le Febvrier, Arnaud
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Barrirero, Jenifer
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Saarland Univ, Germany.
    Muecklich, F.
    Saarland Univ, Germany.
    Boyd, Robert
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Jöesaar Johansson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Dislocation structure and microstrain evolution during spinodal decomposition of reactive magnetron sputtered heteroepixatial c-(Ti-0.37,Al-0.63)N/c-TiN films grown on MgO(001) and (111) substrates2019In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 125, no 10, article id 105301Article in journal (Refereed)
    Abstract [en]

    Heteroepitaxial c-(Ti-0.37,Al-0.63)N thin films were grown on MgO(001) and MgO(111) substrates using reactive magnetron sputtering. High resolution high-angle annular dark-field scanning transmission electron micrographs show coherency between the film and the substrate. In the as-deposited state, x-ray diffraction reciprocal space maps show a strained epitaxial film. Corresponding geometric phase analysis (GPA) deformation maps show a high stress in the film. At elevated temperature (900 degrees C), the films decompose to form iso-structural coherent c-Al- and c-TiN-rich domains, elongated along the elastically soft amp;lt;100amp;gt; directions. GPA analysis reveals that the c-TiN domains accommodate more dislocations than the c-AlN domains. This is because of the stronger directionality of the covalent bonds in c-AlN compared with c-TiN, making it more favorable for the dislocations to accumulate in c-TiN. The defect structure and strain generation in c-(Ti,Al)N during spinodal decomposition is affected by the chemical bonding state and elastic properties of the segregated domains.

  • 115.
    Calamba, Katherine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Lorraine, France.
    Schramm, Isabella
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Saarland University, Germany.
    Johansson Jöesaar, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Ghanbaja, J.
    University of Lorraine, France.
    Pierson, J. F.
    University of Lorraine, France.
    Mucklich, F.
    Saarland University, Germany.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Enhanced thermal stability and mechanical properties of nitrogen deficient titanium aluminum nitride (Ti0.54Al0.46Ny) thin films by tuning the applied negative bias voltage2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 122, no 6, article id 065301Article in journal (Refereed)
    Abstract [en]

    Aspects on the phase stability and mechanical properties of nitrogen deficient (Ti0.54Al0.46)N-y alloys were investigated. Solid solution alloys of (Ti,Al)N were grown by cathodic arc deposition. The kinetic energy of the impinging ions was altered by varying the substrate bias voltage from -30V to -80 V. Films deposited with a high bias value of -80V showed larger lattice parameter, finer columnar structure, and higher compressive residual stress resulting in higher hardness than films biased at -30V when comparing their as-deposited states. At elevated temperatures, the presence of nitrogen vacancies and point defects (anti-sites and self-interstitials generated by the ion-bombardment during coating deposition) in (Ti0.54Al0.46)N-0.87 influence the driving force for phase separation. Highly biased nitrogen deficient films have point defects with higher stability during annealing, which cause a delay of the release of the stored lattice strain energy and then accelerates the decomposition tendencies to thermodynamically stable c-TiN and w-AlN. Low biased nitrogen deficient films have retarded phase transformation to w-AlN, which results in the prolongment of age hardening effect up to 1100 degrees C, i.e., the highest reported temperature for Ti-Al-N material system. Our study points out the role of vacancies and point defects in engineering thin films with enhanced thermal stability and mechanical properties for high temperature hard coating applications. Published by AIP Publishing.

  • 116.
    Calander, N
    et al.
    Chalmers.
    Willander, Magnus
    Chalmers.
    Theory of surface-plasmon resonance optical-field enhancement at prolate spheroids2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, no 9, p. 4878-4884Article in journal (Refereed)
    Abstract [en]

    The optical-field enhancement from plasmon resonance at spheroids is studied by solving Maxwell equations using spheroidal vector wave functions. This treatment is an extension of the Mie theory for spheres. The phase retardation or dephasing effects, as studied by finite-element methods in a previous article, are confirmed. Nevertheless, the optical-field enhancement is shown to be substantial under certain resonance conditions. It is suggested that the positions of the resonances in parameter space are determined by global antenna properties and the magnitude of the field enhancement by local plasmon resonance.

  • 117. Calmels, Lionel
    et al.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Atomic site sensitivity of the energy loss magnetic chiral dichroic spectra of complex oxides2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 7, p. 07D328-Article in journal (Refereed)
    Abstract [en]

    The quantitative analysis of magnetic oxide core level spectra can become complicated when the magnetic atoms are located at several nonequivalent atomic sites in the crystal. This is, for instance, the case for Fe atoms in magnetite, which are located in tetrahedral and octahedral atomic sites; in this case, the x-ray magnetic circular dichroic (XMCD) spectra recorded at the L-2,L-3 edge of Fe contain contributions from the different nonequivalent atomic sites, which unfortunately cannot be separated. Energy loss magnetic chiral dichroic (EMCD) spectra are the transmission electron microscope analogies of the XMCD spectra. One of the important differences between these two techniques of magnetic analysis is that EMCD uses a fast electron beam instead of polarized light. The fast electrons behave like Bloch states in the sample, and the fine structure of the EMCD spectra is strongly influenced by channeling and dynamical diffraction effects. These effects can be adjusted by changing the experimental configuration. We use theoretical calculations, which include dynamical diffraction effects and in which electronic transitions are treated in the atomic multiplet formalism, to show that the relative weight of the Fe atoms in different nonequivalent atomic sites can be changed by a proper choice of the position of the detector and of the magnetite sample orientation and thickness. We conclude that EMCD spectra could be used to isolate the magnetic contribution of atoms in each of the nonequivalent atomic sites, which would not be possible with XMCD techniques. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3556769]

  • 118.
    Canalias, Carlota
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Hirohashi, Junji
    KTH, School of Engineering Sciences (SCI), Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Physics.
    Polarization switching characteristics of flux grown KTiOPO4 and RbTiOPO4 at room temperature2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 12, p. 124105-Article in journal (Refereed)
    Abstract [en]

    A study of polarization-switching characteristics under an applied electrical field at room temperature is presented for flux-grown KTiOPO4 and RbTiOPO4. By optimizing the experimental conditions, we determined the coercive field and the domain-switching time quantitatively by direct observation of the switching current. For both isomorphs, the inverse of the polarization-switching time, 1/t(s), follows an exponential dependence on the applied field E in low-field regime, and a linear dependence on E in the high-field regime. Domain morphology of KTiOPO4 based on selective etching reveals laminar structures elongated in the b crystallographic direction. An estimation of the domain-wall velocity shows that the domain speed in the polar direction is, at least, two orders of magnitude larger than in the a-b plane. The velocity along the b direction is similar to 30 times larger than along the a axis.

  • 119. Carmody, C.
    et al.
    Tan, H. H.
    Jagadish, C.
    Douhéret, Olivier
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Maknys, Kestutis
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Anand, Srinivasan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zou, J.
    Dao, L.
    Gal, M.
    Structural, electrical, and optical analysis of ion implanted semi-insulating InP2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 95, no 2, p. 477-482Article in journal (Refereed)
    Abstract [en]

    Semi-insulating InP was implanted with MeV P, As, Ga, and In ions, and the resulting evolution of structural properties with increased annealing temperature was analyzed using double crystal x-ray diffractometry and cross sectional transmission electron microscopy. The types of damage identified are correlated with scanning spreading resistance and scanning capacitance measurements, as well as with previously measured Hall effect and time resolved photoluminescence results. We have identified multiple layers of conductivity in the samples which occur due to the nonuniform damage profile of a single implant. Our structural studies have shown that the amount and type of damage caused by implantation does not scale with implant ion atomic mass.

  • 120. Carmody, C.
    et al.
    Tan, H. H.
    Jagadish, C.
    Gaarder, A.
    Marcinkevicius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Ultrafast carrier trapping and recombination in highly resistive ion implanted InP2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 2, p. 1074-1078Article in journal (Refereed)
    Abstract [en]

    MeV P+ implanted and annealed p-InP, and Fe+ implanted and annealed semi-insulating InP have both been shown to produce the high resistivity, good mobility, and ultrafast optical response desired for ultrafast photodetectors. Hall effect measurements and time resolved photoluminescence were used to analyze the electrical and optical features of such implanted materials. Low temperature annealing was found to yield the fastest response times-130 fs for Fe+ implanted and 400 fs for P+ implanted InP, as well as resistivities of the order similar to10(6) Omega/square. It was found that the electrical activation of Fe-related centers, useful for achieving high resistivities in Fe+ implanted semi-insulating InP, was not fully realized at the annealing temperatures chosen to produce the fastest optical response. Implanting p-InP in the dose regime where type conversion occurs, and subsequent annealing at 500degreesC, produces high resistivities and ultrafast carrier trapping times that are only marginally dose dependent.

  • 121. Carville, N. C.
    et al.
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Denning, D.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Rodriguez, B. J.
    Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate: Time and concentration dependence2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 18, p. 187212-1-187212-7Article in journal (Refereed)
    Abstract [en]

    Photodeposition of metallic nanostructures onto ferroelectric surfaces, which have been chemically patterned using a proton exchange process, has recently been demonstrated. By varying the molar concentration of the AgNO 3 solution and the illumination time, one can determine the initial nucleation sites, control the rate of nucleation and the height of silver nanostructures formed, and study the mechanisms by which these processes occurs. The nanoparticles are found to deposit preferentially in the boundary between ferroelectric and proton exchanged regions, in an area proton exchanged via lateral diffusion under the masking layer used for chemical patterning, consistent with our previous results. Using a short illumination time (3 min), we are able to determine that the initial nucleation of the silver nanostructure, having a width of 0.17 ± 0.02 μm and a height of 1.61 ± 0.98 nm, occurs near the edge of the reactive ion etched area within this lateral diffusion region. Over longer illumination times (15 min), we find that the silver deposition has spread to a width of 1.29 ± 0.06 μm, extending across the entire lateral diffusion region. We report that at a high molar concentration of AgNO3 (10-2 M), the amount of silver deposition for 5 min UV illumination is greater (2.88 ± 0.58 nm) compared to that at low (10-4 M) concentrations (0.78 ± 0.35 nm), however, this is not the case for longer time periods. With increasing illumination time (15 min), experiments at 10-4 M had greater overall deposition, 6.90 ± 1.52 nm, compared to 4.50 ± 0.76 nm at 10 -2 M. For longer exposure times (30 min) at 10-2 M, the nanostructure height is 4.72 ± 0.59 nm, suggesting a saturation in the nanostructure height. The results are discussed in terms of the electric double layer that forms at the crystal surface. There is an order of magnitude difference between the Debye lengths for 10-2 and 10-4 M solutions, i.e., 3.04 vs. 30.40 nm, which suggests the Debye length plays a role in the availability of Ag ions at the surface.

  • 122. Carville, N. Craig
    et al.
    Neumayer, Sabine M.
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Baghban, Mohammad-Amin
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ivanov, Ilia N.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Rodriguez, Brian J.
    Influence of annealing on the photodeposition of silver on periodically poled lithium niobate2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 5, article id 054102Article in journal (Refereed)
    Abstract [en]

    The preferential deposition of metal nanoparticles onto periodically poled lithium niobate surfaces, whereby photogenerated electrons accumulate in accordance with local electric fields and reduce metal ions from solution, is known to depend on the intensity and wavelength of the illumination and the concentration of the solution used. Here, it is shown that for identical deposition conditions (wavelength, intensity, concentration), post-poling annealing for 10 h at 200 degrees C modifies the surface reactivity through the reorientation of internal defect fields. Whereas silver nanoparticles deposit preferentially on the +z domains on unannealed crystals, the deposition occurs preferentially along 180 degrees domain walls for annealed crystals. In neither case is the deposition selective; limited deposition occurs also on the unannealed -z domain surface and on both annealed domain surfaces. The observed behavior is attributed to a relaxation of the poling-induced defect frustration mediated by Li+ ion mobility during annealing, which affects the accumulation of electrons, thereby changing the surface reactivity. The evolution of the defect field with temperature is corroborated using Raman spectroscopy.

  • 123.
    Castelain, Mickael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rouxhet, Paul G.
    Pignon, Frederic
    Magnin, Albert
    Piau, Jean-Michel
    Single-cell adhesion probed in-situ using optical tweezers: A case study with Saccharomyces cerevisiae2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 11, p. 114701-Article in journal (Refereed)
    Abstract [en]

    A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4723566]

  • 124.
    Castellanos, Sergio
    et al.
    Massachusetts Institute of Technology, Massachusetts, USA.
    Kivambe, Maulid
    Massachusetts Institute of Technology, Massachusetts, USA.
    Hofstetter, Jasmin
    Massachusetts Institute of Technology, Massachusetts, USA.
    Rinio, Markus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Lai, Barry
    Argonne Photon Source, Illinois, USA.
    Buonassisi, Tonio
    Massachusetts Institute of Technology, Massachusetts, USA.
    Variation of dislocation etch-pit geometry: An indicator of bulk microstructure and recombination activity in multicrystalline silicon2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 18, p. 1-7, article id 183511Article in journal (Refereed)
    Abstract [en]

    Dislocation clusters in multicrystalline silicon limit solar cell performance by decreasing minoritycarrier diffusion length. Studies have shown that the recombination strength of dislocation clusterscan vary by up to two orders of magnitude, even within the same wafer. In this contribution, wecombine a surface-analysis approach with bulk characterization techniques to explore theunderlying root cause of variations in recombination strength among different clusters. We observethat dislocation clusters with higher recombination strength consist of dislocations with a largervariation of line vector, correlated with a higher degree of variation in dislocation etch-pit shapes(ellipticities). Conversely, dislocation clusters exhibiting the lowest recombination strength containmostly dislocations with identical line vectors, resulting in very similar etch-pit shapes. Thedisorder of dislocation line vector in high-recombination clusters appears to be correlated withimpurity decoration, possibly the cause of the enhanced recombination activity. Based on ourobservations, we conclude that the relative recombination activity of different dislocation clustersin the device may be predicted via an optical inspection of the distribution and shape variation ofdislocation etch pits in the as-grown wafer.

  • 125.
    Castro Meira, M. V.
    et al.
    University of Federal Reconcavo Bahia, Brazil University of Federal Bahia, Brazil .
    Ferreira da Silva, A.
    University of Federal Bahia, Brazil .
    Baldissera, G.
    Royal Institute Technology, Sweden .
    Persson, C.
    Royal Institute Technology, Sweden University of Oslo, Norway .
    Freitas, J. A.
    USN, USA .
    Gutman, N.
    Hebrew University of Jerusalem, Israel Hebrew University of Jerusalem, Israel .
    Saar, A.
    Hebrew University of Jerusalem, Israel Hebrew University of Jerusalem, Israel .
    Nur, Omer
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Optical characterization of ZnO nanopillars on Si and macroporous periodic Si structure2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 12, p. 123527-Article in journal (Refereed)
    Abstract [en]

    ZnO nanopillars were successfully grown using both the vapor-liquid-solid and the aqueous chemical growth methods on different substrates, such as quartz, n-, and p-type non-porous Si wafer (flat) and microporous periodic Si structure (MPSiS). Scanning electron microscopy was employed to compare sample morphologies. The absorption was calculated employing the GW(0) method, based on the local density approximation, and with the projector augmented wave approach. Experiment and theory show a reasonable agreement when the shape of the optical absorption is considered. The measured absorption of ZnO nanopillars, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the energy gap spectral range. A strong effect of MPSiS substrates on ZnO nanopillar properties is observed. The photoluminescence technique was also employed as an optical characterization.

  • 126. Castro Meira, M. V.
    et al.
    Ferreira da Silva, A.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Freitas, J. A., Jr.
    Gutman, N.
    Sa'ar, A.
    Nur, O.
    Willander, M.
    Optical characterization of ZnO nanopillars on Si and macroporous periodic Si structure2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 12, p. 123527-Article in journal (Refereed)
    Abstract [en]

    ZnO nanopillars were successfully grown using both the vapor-liquid-solid and the aqueous chemical growth methods on different substrates, such as quartz, n-, and p-type non-porous Si wafer (flat) and microporous periodic Si structure (MPSiS). Scanning electron microscopy was employed to compare sample morphologies. The absorption was calculated employing the GW(0) method, based on the local density approximation, and with the projector augmented wave approach. Experiment and theory show a reasonable agreement when the shape of the optical absorption is considered. The measured absorption of ZnO nanopillars, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the energy gap spectral range. A strong effect of MPSiS substrates on ZnO nanopillar properties is observed. The photoluminescence technique was also employed as an optical characterization.

  • 127. Cederkrantz, D.
    et al.
    Farahi, N.
    Borup, K. A.
    Iversen, B. B.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Palmqvist, A. E. C.
    Enhanced thermoelectric properties of Mg2Si by addition of TiO2 nanoparticles2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 2, article id 023701Article in journal (Refereed)
    Abstract [en]

    The effects on the thermoelectric properties of Mg2Si when adding TiO2 nanoparticles have been evaluated experimentally. A batch of Mg2Si was prepared through direct solid state reaction and divided into portions which were mechanically mixed with different amounts of TiO2 nanoparticles ranging from 0.5 to 3 vol% and subsequently sintered to disks. All materials showed n-type conduction and the absolute value of the Seebeck coefficient was reduced with increasing amount of TiO2 added, while the electrical resistivity was greatly reduced. The thermal conductivity was surprisingly little affected by the addition of the nanoparticles. An optimum value of the thermoelectric figure-of-merit ZT = TS2 sigma/k was found for the addition of 1 vol% TiO2, showing almost three times higher ZT value than that of the pure Mg2Si. Larger TiO2 additions resulted in lower ZT values and with 3 vol% added TiO2 the ZT was comparable to the pure Mg2Si. The sintering process resulted in reduction or chemical reaction of all TiO2 to TiSi2 and possibly elemental titanium as well as reduced TiOx. The increased electrical conductivity and the decreased Seebeck coefficient were found due to an increased charge carrier concentration, likely caused by the included compounds or titanium-doping of the Mg2Si matrix. The low observed effect on the thermal conductivity of the composites may be explained by the relatively higher thermal conductivity of the included compounds, counter-balancing the expected increased grain boundary scattering. Alternatively, the introduction of compounds does not significantly increase the concentration of scattering grain boundaries.

  • 128. Cederkrantz, D.
    et al.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Palmqvist, A. E. C.
    Thermoelectric properties of partly Sb- and Zn-substituted Ba(8)Ga(16)Ge(30) clathrates2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 11, p. 113711-Article in journal (Refereed)
    Abstract [en]

    The effects on the thermoelectric properties of n-Ba(8)Ga(16)Ge(30) when substituting small amounts of the Ga or Ge with Sb or Zn have been investigated. A number of syntheses were prepared in quaternary systems of Ba(8)Ga(16)Ge(30) substituted with either Sb or Zn but only three samples were found to yield single phase products with nominal compositions of Ba(8)Ga(15)Sb(1)Ge(30), Ba(8)Ga(15)Zn(1)Ge(30) and Ba(8)Ga(16)Ge(28)Zn(2), respectively. When Ge was substituted for Zn the resulting sample remained n-type and an increase in thermopower and a decrease in thermal conductivity were achieved. These positive effects were accompanied with an increased electrical resistivity and thus the ZT was only somewhat improved up to about 400 degrees C. When substituting Ga with either Sb or Zn samples remained n-type but showed decreased thermopower and increased electrical resistivity and thermal conductivity. It is thus concluded that substitution of Ga with Zn or Sb is detrimental for the thermoelectric properties of Ba(8)Ga(16)Ge(30), whereas substitution of Ge with Zn appears a potent method for improving its performance.

  • 129. Celzard, Alain
    et al.
    McRae, Edward
    Marêché, Jean-Francois
    Furdin, Guy
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Conduction mechanisms in some graphite-polymer composites: effects of temperature and pressure1998In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 83, no 3, p. 1410-1419Article in journal (Refereed)
    Abstract [en]

    This article is devoted to the conduction mechanisms involved in some highly electrically anisotropic resin–graphite particle composites. These materials are known to show a percolation phenomenon as the filler content is varied; they are epoxy or polyurethane based, the conducting particles are oriented single-crystal platelets, and samples are in the form of thick films. Because of their strong anisotropy, two types of measurements were made, i.e., parallel to and perpendicular to the plane of the films. Study of the resistivity variations of samples containing various concentrations in conducting particles was carried out first as a function of temperature from 4.2 to 300 K at ambient pressure, and second as a function of hydrostatic pressure up to 1.2 GPa, at room temperature. As the temperature is varied, the changes in resistivity of all the samples studied (i.e., above percolation threshold) are weak; analysis leads to the conclusion that thermally activated tunneling plays a dominant role above but close to the percolation threshold phic. As a function of pressure, more samples were studied: when the filler content is above phic, resistivity changes are quantitatively in agreement with what is expected from both percolation theory and tunneling; below threshold, the observed behavior is partially attributable to an ionic conduction mechanism throughout the polymer.

  • 130.
    Chason, E.
    et al.
    Brown University, USA.
    Karlson, M.
    Brown University, USA.
    Colin, J. J.
    University of Poitiers, France.
    Magnfält, Daniel
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Sarakinos, Kostas
    Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
    Abadias, G.
    University of Poitiers, France.
    A kinetic model for stress generation in thin films grown from energetic vapor fluxes2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 14, article id 145307Article in journal (Refereed)
    Abstract [en]

    We have developed a kinetic model for residual stress generation in thin films grown from energetic vapor fluxes, encountered, e.g., during sputter deposition. The new analytical model considers sub-surface point defects created by atomic peening, along with processes treated in already existing stress models for non-energetic deposition, i.e., thermally activated diffusion processes at the surface and the grain boundary. According to the new model, ballistically induced subsurface defects can get incorporated as excess atoms at the grain boundary, remain trapped in the bulk, or annihilate at the free surface, resulting in a complex dependence of the steady-state stress on the grain size, the growth rate, as well as the energetics of the incoming particle flux. We compare calculations from the model with in situ stress measurements performed on a series of Mo films sputter-deposited at different conditions and having different grain sizes. The model is able to reproduce the observed increase of compressive stress with increasing growth rate, behavior that is the opposite of what is typically seen under non-energetic growth conditions. On a grander scale, this study is a step towards obtaining a comprehensive understanding of stress generation and evolution in vapor deposited polycrystalline thin films. Published by AIP Publishing.

  • 131. Chawla, Amit Kumar
    et al.
    Singhal, Sonal
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Gupta, Hari Om
    Chandra, Ramesh
    Study of composition dependent structural, optical, and magnetic properties of Cu-doped Zn1-xCdxS nanoparticles2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 12, p. 123519-Article in journal (Refereed)
    Abstract [en]

    Cu-doped Zn1-xCdxS nanoparticles were synthesized by coprecipitation technique in ice bath at 280 K. The band gap energy of Zn1-xCdxS:Cu nanoparticles can be tuned to a lower energy by increasing the Cd content, indicating the formation of the alloyed nanoparticles. The alloy structure is further supported by the systematic shifting of characteristic x-ray diffraction peaks to lower angles with increase in Cd content. Systematic copper doping induces a red shift in the energy band gap of Zn0.9Cd0.1S:Cu nanoparticles with increase in copper concentration. Cu-doped Zn0.9Cd0.1S nanoparticles were found to have ferromagnetic nature at 5 K whereas undoped particles were found to be diamagnetic. Green luminescence further proves proper doping of Cu into the ZnCdS matrix. It is believed that the green luminescence originates from the recombination between the shallow donor level (sulfur vacancy) and the t(2) level of Cu2+. This method provides an inexpensive and simple procedure to produce ternary ZnCdS: Cu nanoparticles with tunable optical properties via changing Cd and/or Cu concentrations.

  • 132.
    Chen, Jr-Tai
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hsu, Chih-Wei
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 8, article id 085301Article in journal (Refereed)
    Abstract [en]

    Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H2 atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm2/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 1020 cm−3 at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm2 SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

  • 133.
    Chen, K.
    et al.
    Nanjing University, Peoples R China.
    Li, G. L.
    Nanjing University, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Liu, J.
    Nanjing University, Peoples R China.
    Liu, J. M.
    Nanjing University, Peoples R China.
    Zhu, J. S.
    Nanjing University, Peoples R China.
    Conducting grain boundaries in the high-dielectric-constant ceramic CaCu3Ti4O122007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 7, p. 074101-Article in journal (Refereed)
    Abstract [en]

    To clarify the electrical property of grain boundaries, the fine-grained ceramics CaCu3Ti4O12 have been treated with the hydrofluoric acid to remove the parts of grain boundaries. The dielectric response difference between the etched samples and the pristine ones indicates that the ceramic CaCu3Ti4O12 consists of insulating or semiconducting grains with conducting grain boundaries. Therefore, the giant dielectric phenomenon is supposed not to derive from the grain boundary barrier layer capacitance effect. The possible mechanism is discussed. (c) 2007 American Institute of Physics.

  • 134.
    Chen, K.
    et al.
    Nanjing University, Peoples R China.
    Yuan, S. K.
    Nanjing University, Peoples R China.
    Li, P. L.
    Nanjing University, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Liu, J.
    Nanjing University, Peoples R China.
    Li, G. L.
    Nanjing University, Peoples R China.
    Zhao, A. G.
    Nanjing University, Peoples R China.
    Lu, X. M.
    Nanjing University, Peoples R China.
    Liu, J. M.
    Nanjing University, Peoples R China.
    Zhu, J. S.
    Nanjing University, Peoples R China.
    High permittivity in zr doped NiO ceramics2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 3, p. 034103-Article in journal (Refereed)
    Abstract [en]

    We report on measurements of the dielectric permittivity of NiO-based ceramics doped with Zr (ZNO). Samples were prepared by the traditional solid-state reaction method. The concentration of Zr has an effect on the dielectric properties of ZNO ceramics. High permittivity values (similar to 10(4)) were observed which remain almost constant from 200 K to 350 K at low frequencies. The high-dielectric-constant response of the ZNO ceramics is attributed mainly to a grain boundary (internal) barrier layer capacitance. (c) 2007 American Institute of Physics.

  • 135.
    Chen, Rongzhen
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Band-edge density-of-states and carrier concentrations in intrinsic and p-type CuIn1-xGaxSe22012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 10, p. 103708-Article in journal (Refereed)
    Abstract [en]

    The electronic structures of chalcopyrite CuIn1-xGaxSe2 have recently been reported to have strongly anisotropic and non-parabolic valence bands (VBs) even close to the Gamma-point VB maximum. Also, the lowest conduction band (CB) is non-parabolic for energies 50-100 meV above the CB minimum. The details in the band-edge dispersion govern the material's electrical properties. In this study, we, therefore, analyze the electronic structure of the three uppermost VBs and the lowest CB in CuIn1-xGaxSe2 (x = 0, 0.5, and 1). The parameterized band dispersions are explored, and the density-of-states (DOS) as well as the constant energy surfaces are calculated and analyzed. The carrier concentration and the Fermi energy E-F in the intrinsic alloys as functions of the temperature is determined from the DOS. The carrier concentration in p-type materials is modeled by assuming the presence of Cu vacancies as the acceptor type defect. We demonstrate that the non-parabolicity of the energy bands strongly affects the total DOS. Therefore, it is important to take into account full band dispersion of the VBs and CB when analyzing the free carrier concentration, like for instance, in studies of electronic transport and/or measurements that involve strong excitation conditions.

  • 136.
    Chen, Rongzhen
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norge.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norge.
    Electronic and optical properties of Cu2 X SnS4 (X = Be, Mg, Ca, Mn, Fe, and Ni) and the impact of native defect pairs2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 20, article id 203104Article in journal (Refereed)
    Abstract [en]

    Reducing or controlling cation disorder in Cu2ZnSnS4 is a major challenge, mainly due to low formation energies of the anti-site pair (Cu Zn - + Zn Cu +) and the compensated Cu vacancy (V Cu - + Zn Cu +). We study the electronic and optical properties of Cu2XSnS4 (CXTS, with X = Be, Mg, Ca, Mn, Fe, and Ni) and the impact of defect pairs, by employing the first-principles method within the density functional theory. The calculations indicate that these compounds can be grown in either the kesterite or stannite tetragonal phase, except Cu2CaSnS4 which seems to be unstable also in its trigonal phase. In the tetragonal phase, all six compounds have rather similar electronic band structures, suitable band-gap energies Eg for photovoltaic applications, as well as good absorption coefficients α(ω). However, the formation of the defect pairs (C u X + X Cu) and (V Cu + X Cu) is an issue for these compounds, especially considering the anti-site pair which has formation energy in the order of ∼0.3 eV. The (C u X + X Cu) pair narrows the energy gap by typically ΔEg ≈ 0.1-0.3 eV, but for Cu2NiSnS4, the complex yields localized in-gap states. Due to the low formation energy of (C u X + X Cu), we conclude that it is difficult to avoid disordering from the high concentration of anti-site pairs. The defect concentration in Cu2BeSnS4 is however expected to be significantly lower (as much as ∼104 times at typical device operating temperature) compared to the other compounds, which is partly explained by larger relaxation effects in Cu2BeSnS4 as the two anti-site atoms have different sizes. The disadvantage is that the stronger relaxation has a stronger impact on the band-gap narrowing. Therefore, instead of trying to reduce the anti-site pairs, we suggest that one shall try to compensate (C u X + X Cu) with (V Cu + X Cu) or other defects in order to stabilize the gap energy.

  • 137. Chen, X. W.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Choy, W. C. H.
    Highly efficient and tunable fluorescence of a nanofluorophore in silica/metal dual shells with plasmonic resonance2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 2Article in journal (Refereed)
    Abstract [en]

    A dual-shell structure consisting of a silica buffer shell and a metallic outer shell is studied and designed for highly efficient and tunable fluorescence. The enhanced Purcell effect due to the plasmonic resonance and the dependence of the resonance on the structural parameters are analyzed and discussed through a classical electromagnetic approach. With the present dual-shell structure a fivefold enhancement of the fluorescence efficiency can be achieved for a nanofluorophore comprised of multiple tetramethylrhodamine isothiocyanate dye molecules, as compared to the nanofluorophore within a single silica shell. Furthermore, the peak wavelength of the fluorescence spectrum can be tuned easily (due to the variation of the surface plasmon resonance) by over 50 nm when the refractive index of the ambient material varies from 1.3 to 1.6.

  • 138. Chen, Xue-Wen
    et al.
    Choy, Wallace C. H.
    He, Sailing
    Chui, P. C.
    Comprehensive analysis and optimal design of top-emitting organic light-emitting devices2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 11Article in journal (Refereed)
  • 139.
    Chen, Yafeng
    et al.
    Hokkaido Univ, Japan.
    Kiba, Takayuki
    Kitami Inst Technol, Japan.
    Takayama, Junichi
    Hokkaido Univ, Japan.
    Higo, Akio
    Tohoku Univ, Japan.
    Tanikawa, Tomoyuki
    Tohoku Univ, Japan.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Samukawa, Seiji
    Tohoku Univ, Japan.
    Murayama, Akihiro
    Hokkaido Univ, Japan.
    Temperature-dependent radiative and non-radiative dynamics of photo-excited carriers in extremely high-density and small InGaN nanodisks fabricated by neutral-beam etching using bio-nano-templates2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 20, article id 204305Article in journal (Refereed)
    Abstract [en]

    Temperature-dependent radiative and non-radiative dynamics of photoexcited carriers were studied in In0.3Ga0.7N nanodisks (NDs) fabricated from quantum wells (QWs) by neutral-beam etching using bio-nano-templates. The NDs had a diameter of 5 nm, a thickness of 2 and 3 nm, and a sheet density of 2 x 10(11) cm(-2). The radiative decay time, reflecting the displacement between the electron and hole wavefunctions, is about 0.2 ns; this value is almost constant as a function of temperature in the NDs and not dependent on their thickness. We observed non-exponential decay curves of photoluminescence (PL) in the NDs, particularly at temperatures above 150 K. The thermal activation energies of PL quenching in the NDs are revealed to be about 110 meV, corresponding to the barrier heights of the valence bands in the disks. Therefore, hole escape is deemed responsible for the PL quenching, while thermal activation energies of 12 meV due to the trapping of carriers by defects were dominant in the mother QWs. The above-mentioned non-exponential PL decay curves can be attributed to variations in the rate of hole escape in the NDs because of fluctuations in the valence-band barrier height, which, in turn, is possibly due to compositional fluctuations in the QWs. We found that non-radiative trapping, characteristic of the original QW, also exists in about 1% of the NDs in a form that is not masked by other newly formable defects. Therefore, we suggest that additional defect formation is not significant during our ND fabrication process. Published by AIP Publishing.

  • 140.
    Chernogorova, O.
    et al.
    Baikov Institute of Metallurgy and Materials Science (IMET), Russian Academy of Sciences.
    Drozdova, E.
    Baikov Institute of Metallurgy and Materials Science (IMET), Russian Academy of Sciences.
    Ovchinnikova, I.
    Baikov Institute of Metallurgy and Materials Science (IMET), Russian Academy of Sciences.
    Soldatov, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ekimov, E.
    Vereshchagin Institute for High Pressure Physics RAS, Troitsk.
    Structure and properties of superelastic hard carbon phase created in fullerene-metal composites by high temperature-high pressure treatment2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 11Article in journal (Refereed)
    Abstract [en]

    Treatment of a fullerene soot extract and metal (Co) powder mixture under pressure of 5 and 8 GPa at 1000 °C leads to the transformation of fullerites into superelastic hard phase (SHP) and to simultaneous sintering of the powder mixture to nonporous composite material reinforced by the SHP particles. The structure of the SHP particles reveals a topological relation to the initial fullerite crystal morphology. Upon indentation, the SHP particles demonstrate an elastic recovery of up to 96. The universal microhardness of the SHP particles HU=26 GPa, and their microhardness HV = 35 GPa. A high ratio between the microhardness and elastic modulus (HV/E = 0.19-0.21) of the SHP particles makes them perspective candidates for design of materials with superior wear resistance and tribological properties.

  • 141.
    Chijioke, Akobuije D.
    et al.
    Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts.
    Nellis, W. J.
    Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts.
    Soldatov, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Silvera, Isaac F.
    Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts.
    The ruby pressure standard to 150 GPa2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 11, p. 1-9Article in journal (Refereed)
    Abstract [en]

    A determination of the ruby high-pressure scale is presented using all available appropriate measurements including our own. Calibration data extend to 150 GPa. A careful consideration of shock-wave-reduced isotherms is given, including corrections for material strength. The data are fitted to the calibration equation P=(A/B)[(/0)B–1] (GPa), with A=1876±6.7, B=10.71±0.14, and is the peak wavelength of the ruby R1 line.

  • 142. Cho, C. R.
    et al.
    Grishin, Alexander M.
    KTH, Superseded Departments, Physics.
    Background oxygen effects on pulsed laser deposited Na0.5K0.5NbO3 films: From superparaelectric state to ferroelectricity2000In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 87, no 9, p. 4439-4448Article in journal (Refereed)
    Abstract [en]

    Ambient oxygen pressure in a pulsed laser deposition process has been observed to have a critical influence on the compositional, crystalline, and electrical properties of Na0.5K0.5NbO3 (NKN) thin films grown onto polycrystalline Pt80Ir20 and SiO2 (native oxide)/Si(111) substrates. Films prepared at high oxygen pressure (similar to 400 mTorr) were found to be single phase and highly c-axis oriented. X-ray diffraction theta-2 theta scans and rocking curve data show a strong effect of NKN film self-assembling along the [001] direction regardless of the substrate texture. The high dielectric permittivity of 550, low dissipation factor of less than 3%, and high remanent polarization of 12 mu C/cm(2) indicate the high ferroelectric quality of the fabricated film. The role of the high-energy component of the erosion products has been proven to be crucial to film performance. On the other hand, films grown at low oxygen pressure (similar to 10 mTorr) have been found to be mixed phases of ferroelectric NKN and paraelectric potassium niobates. These films have shown superparaelectric behavior: 5% tunability at an electric field of 100 kV/cm, losses as low as 0.3%, and excellent stability to temperature and frequency changes.

  • 143. Choi, I. S.
    et al.
    An, S. Y.
    Chung, S. J.
    Lee, S.
    Liu, X.
    Furdyna, J.
    Transport properties of ferromagnetic GaMnAs interfaced with paramagnetic ZnMnSe in the form of bilayer structures2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, no 8Article in journal (Refereed)
    Abstract [en]

    We have investigated the magnetotransport properties of a series of magnetic semiconductor bilayer structures consisting of 300-nm-thick Ga1-x Mnx As and 150-nm-thick Zn1-y Mny Se layers. The temperature scan of resistance and an Arrot plot obtained from Hall resistance data showed that the Curie temperature (TC) of the GaMnAsZnMnSe bilayer is higher than that of the bare GaMnAs. Furthermore, magnetoresistance measurement reveals significant enhancement of the magnetic hardness of the GaMnAs system in bilayer form even though the magnetic easy axis of the GaMnAs was not altered by the neighboring ZnMnSe layer. This observation indicates that the magnetotransport properties of GaMnAs can be changed by an adjacent magnetic layer due to the interactions between the two magnetic layers. © 2006 American Institute of Physics.

  • 144. Choi, S. G.
    et al.
    Zhao, H. Y.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Perkins, C. L.
    Donohue, A. L.
    To, B.
    Norman, A. G.
    Li, J.
    Repins, I. L.
    Dielectric function spectra and critical-point energies of Cu2ZnSnSe4 from 0.5 to 9.0 eV2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 3, p. 033506-Article in journal (Refereed)
    Abstract [en]

    We present dielectric function epsilon=epsilon(1) + i epsilon(2) spectra and critical-point energies of Cu2ZnSnSe4 determined by spectroscopic ellipsometry from 0.5 to 9.0 eV. We reduce artifacts from surface overlayers to the maximum extent possible by performing chemical-mechanical polishing and wet-chemical etching of the surface of a Cu2ZnSnSe4 thin film. Ellipsometric data are analyzed by the multilayer model and the epsilon spectra are extracted. The data exhibit numerous spectral features associated with critical points, whose energies are obtained by fitting standard lineshapes to second energy derivatives of the data. The experimental results are in good agreement with the a spectra calculated within the GW quasi-particle approximation, and possible origins of the pronounced critical-point structures are identified.

  • 145. Christensen, JS
    et al.
    Radamson, Henry H.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kuznetsov, AY
    Svensson, BG
    Diffusion of phosphorus in relaxed Si1-xGex films and strained Si/Si1-xGex heterostructures2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 10, p. 6533-6540Article in journal (Refereed)
    Abstract [en]

    Phosphorus diffusion has been studied in relaxed Si1-xGex samples (x=0.11 and 0.19) and strained Si/Si1-xGex/Si heterostructures (x=0.08, 0.13, and 0.18). The diffusivity of P is found to increase with increasing Ge content, while the influence of compressive strain results in a decrease in diffusivity as compared to that in relaxed material. The effect of strain is found to be equivalent to an apparent activation energy of -13 eV per unit strain, where the negative sign indicates that the P diffusion is mediated by interstitials in Si1-xGex (x<0.20). This conclusion is also supported by an experiment utilizing injection of Si self-interstitials, which results in an enhanced P diffusion in strained Si1-xGex. Further, P is found to segregate into Si across Si/Si1-xGex interfaces and the segregation coefficient increases with increasing Ge concentration.

  • 146. Christensen, M
    et al.
    Iversen, BB
    Bertini, L
    Gatti, C
    Toprak, Muhammet S.
    KTH, Superseded Departments, Materials Science and Engineering.
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Nishibori, E
    Structural study of Fe doped and Ni substituted thermoelectric skutterudites by combined synchrotron and neutron powder diffraction and ab initio theory2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 6, p. 3148-3157Article in journal (Refereed)
    Abstract [en]

    We present neutron and synchrotron powder-diffraction investigations as well as ab initio calculations to elucidate delicate structural features in doped skutterudites. Samples with assumed Fe doping were investigated (FeyCo4Sb12, y=0.4, 0.8, 1.0, and 1.6), as well as samples with formal Ni substitution (Co4-xNixSb12, x=0, 0.4, 0.8, and 1.2). The present study serves as a case story for the determination of fine structural details of thermoelectric skutterudites by diffraction methods in combination with ab initio calculations. We illustrate the problem of fluorescence in the conventional x-ray powder diffraction on the Fe-doped samples by a comparison with the neutron powder-diffraction data. On the series of the Ni-substituted samples, the neutron powder-diffraction data were collected to investigate the exact sitting of the Ni. The sample with the highest Ni substitution (Co2.8Ni1.2Sb12) was also used for high resolution, high-energy synchrotron powder diffraction measurements. These revealed that the sample consists of two skutterudite phases. A complete description of the Ni-substituted samples was obtained in tandem with ab initio calculations, which show that the system contains a Ni-rich (Co0.38Ni3.62Sb12) and a Ni-poor (Co3.76Ni0.24Sb12)) skutterudite phases.

  • 147. Chung, J. -H
    et al.
    Song, Y. -S
    Yoo, T.
    Chung, S. J.
    Department of Physics, Korea University.
    Lee, S.
    Kirby, B. J.
    Liu, X.
    Furdyna, J. K.
    Investigation of weak interlayer exchange coupling in GaMnAs/GaAs superlattices with insulating nonmagnetic spacers2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 1Article in journal (Refereed)
    Abstract [en]

    A robust long-range antiferromagnetic coupling between ferromagnetic Ga 0.97Mn 0.03As layers has previously been realized via insertion of nonmagnetic Be-doped GaAs spacers between the magnetic layers. In this paper we report the observation of weak antiferromagnetic coupling between Ga 0.97Mn 0.03As layers through undoped GaAs spacers with thicknesses as large as 25 monolayers. The field and the temperature dependences of the sample magnetization suggest that the interlayer coupling in these systems substantially deviates from typical ferromagnetic behavior. Polarized neutron reflectivity measurements reveal antiferromagnetic alignment between Ga 0.97Mn 0.03As layers when a weak field is applied perpendicular to the magnetic easy axis during cooling below T C. The strength of the observed coupling between the magnetic layers is estimated to be weaker than 0.05 mT. © 2011 American Institute of Physics.

  • 148.
    Chung, S. J.
    et al.
    Department of Physics, Korea University.
    Lee, S.
    Park, I. W.
    Liu, X.
    Furdyna, J. K.
    Possible indication of interlayer exchange coupling in GaMnAs/GaAs ferromagnetic semiconductor superlattices2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 95, no 11, p. 7402-7404Article in journal (Refereed)
    Abstract [en]

    The effects of free carriers in the nonmagnetic spacer layer on the magnetic properties of GaMnAs/GaAs ferromagnetic semiconductor superlattices (SL) were investigated. In the SL system, one of the SL structures was doped with Be in the GaAs spacer layers, and the GaAs layer of the other SL were undoped in order to investigate the effects of carriers. The remanent magnetization of the two SL were calculated in order to analyze the robustness of the SL systems. The hardness of the magnetization in the SL with Be-doped GaAs layer was found to be related to interlayer coupling which was introduced by doping of the nonmagnetic layers.

  • 149. Chung, S.
    et al.
    Mohseni, S. M.
    Sani, S. R.
    Iacocca, E.
    Dumas, R. K.
    Nguyen, T. N. Anh
    Pogoryelov, Ye.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Muduli, P. K.
    Eklund, A.
    Hoefer, M.
    Akerman, J.
    Spin transfer torque generated magnetic droplet solitons (invited)2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 17Article in journal (Refereed)
    Abstract [en]

    We present recent experimental and numerical advancements in the understanding of spin transfer torque generated magnetic droplet solitons. The experimental work focuses on nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has an easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The NC-STO resistance and microwave signal generation are measured simultaneously as a function of drive current and applied perpendicular magnetic field. Both exhibit dramatic transitions at a certain current dependent critical field value, where the microwave frequency drops 10 GHz, modulation sidebands appear, and the resistance exhibits a jump, while the magnetoresistance changes sign. We interpret these observations as the nucleation of a magnetic droplet soliton with a large fraction of its magnetization processing with an angle greater than 90 degrees, i.e., around a direction opposite that of the applied field. This interpretation is corroborated by numerical simulations. When the field is further increased, we find that the droplet eventually collapses under the pressure from the Zeeman energy. (C) 2014 AIP Publishing LLC.

  • 150.
    Chung, Sunjae
    et al.
    Department of Physics, Korea University.
    Lee, Sangyeop
    Lee, Hakjoon
    Yoo, Taehee
    Lee, Sanghoon
    Liu, X.
    Furdyna, J. K.
    Investigation of superlattices based on ferromagnetic semiconductor GaMnAs by planar Hall effect2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 7, p. 07D310-1-07D310-3Article in journal (Refereed)
    Abstract [en]

    Two ferromagnetic semiconductor GaMnAs-based superlattices (SLs) were investigated by measuring the planar Hall effect (PHE) with the external magnetic field applied in the plane of the sample. The two GaMnAs/GaAs SLs differed only by the Be doping of the nonmagnetic GaAs spacer layers. Both SLs showed a typical two-step transition behavior in PHE field scans at 4.0 K, essentially the same as that normally observed on single GaMnAs ferromagnetic layers with two in-plane magnetic easy axes. As the temperature increased to 30 K, the behaviors of the PHE changed differently in the two SL samples. The PHE in the undoped SL can be described simply by the temperature dependence of the magnetic anisotropy within the film plane of a GaMnAs film. However, the Be-doped SL revealed a completely different behavior, showing a transition of magnetization with a negative coercive field. The observation of this feature in a ferromagnetic multilayer indicates the presence of spontaneous anti-parallel interlayer exchange coupling between the GaMnAs magnetic layers.

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